Those processes involved in the determination of specific cell fates are fundamental aspects of embryogenesis. In vertebrate embryos, specific tissue interactions, termed inductive interactions, play a major role in the determination of various cell fates. The general goal of our research is to the molecular and cellular basis of these processes. Vertebrate lens development has proved to be an excellent system in which to examine these events, since the development of this organ is triggered by a series of specific tissue inter-actions. The success of this system is due, in part, to its accessibility to direct experimental manipulation, particularly in amphibian embryos. Our understanding of the tissue interactions involved in vertebrate lens induction is extensive, however, virtually nothing is known about the molecular basis for the process of lens cell determination, or the signal molecules involved in lens induction. These issues are the main focus of the current research proposal. Efforts will be devoted to identifying specific changes in gene expression which are associated with the processes of lens cell determination and differentiation using the amphibian Xenopus laevis. It would be very difficult to isolate these genes directly from minute presumptive lens ectodermal tissues during early development. In Xenopus, lenses will regenerate from the larval cornea following lens removal, a process of transdifferentiation. At some level, those genes expressed during the process of lens regeneration should be the same as those expressed during the process of embryonic lens formation. The phenomenon of lens regeneration, will be utilized as a more convenient means to isolate genes involved in the processes of lens cell determination and differentiation. Two cDNA libraries will be prepared from regenerating and non-regenerating corneas. Genes specific to the process of lens regeneration will be isolated using the technique of subtractive hybridization. Once these genes are isolated, their expression will be studied during the process of embryonic lens formation, and specific tests will be conducted to determine whether these genes play an active role in this process. Finally, these genes will be used as markers indicative of early stages of lens development in tissue culture experiments to examine the role that specific lens inductive interactions play in triggering specific changes in gene expression. In addition, tissue culture experiments will be conducted to address questions raised by previous studies, which suggest that inhibitory effects of neural crest cells play a role in pinpointing the exact site of lens differentiation in head ectoderm. Finally, experiments will be performed to determine whether specific growth factors can elicit lens formation in cultures of embryonic ectodermal tissues. There is growing evidence that growth factors play a role in various aspects of embryonic cell determination.